The major efforts of this project are directed at developing therapeutic tools capable of controlling the molecular events in the life cycle of human immunodeficiency viruses (HIV-1 and HIV-2), especially type 1. This study focuses on HIV-2 multi-genic retroviral vectors required for efficient gene delivery to human cells and their application in ex-vivo gene therapy. In this approach we evaluated systematically various factors influencing gene expression in dual gene HIV-2 vectors (Sadaie et al, Human Gene Therapy, submitted, 1995). These vectors are being utilized to deliver the sFv antibodies into susceptible human lymphocytic cells, and study their ability of regulated and sustained expression, and integration into host DNA for stable expression.